1. Field of the Invention
This invention relates to the production of poly(bromoalkenyl aromatics), such as poly(bromostyrenes), by cationic polymerization of the monomers in the presence of a Lewis acid catalyst and an aromatic chain transfer agent.
2. Description of the Prior Art
Polystyrene resins containing bromine atoms on the aromatic ring nucleus have become of greater interest in recent years because of their flame retardancy properties. For instance, brominated styrene oligomers have been disclosed for use as flame retardant materials with nylon molding resins in U.S. Pat. No. 4,137,212 (Theysohn, et al.), and with linear polyester resins in U.S. Pat. No. 4,107,231 (Wurmb, et al.). Bromine-containing styrene oligomers and polymers have also been proposed for use with polyphenylene ether (oxide) resins, essentially for this same purpose.
The development of styrene polymerization has an extended history, and various procedures, including those involving cationic polymerization, have become known over the years. A survey of the art in the ENCYLOPEDIA OF POLYMER SCIENCE AND TECHNOLOGY, John Wiley and Sons, Inc., Volume 3, pages 36 to 37 and page 603 (1965), reports some of the knowledge collected about the cationic polymerization of styrene and related compounds. It is known, for instance, that styrene can be produced in this manner in an organic solvent, using various Lewis acid catalysts. Monomers such as styrene, .alpha.-methylstyrene, indene and acenaphthylene can be polymerized cationically to high molecular weight products, but such processes have no commercial interest. Further, if styrene is cationically polymerized in toluene in particular, the resulting polymers have markedly lower molecular weights than if the polymerization is carried out in, say, carbon tetrachloride.
U.S. Pat. No. 4,143,221 (Naarmann, et al.) discloses a method for the production of styrene polymers or copolymers containing bromine by cationic polymerization of the monomer or comonomers, in an organic solvent, for example, a halohydrocarbon such as 1,2-dichloroethane, in the presence of a Lewis acid catalyst. The method is continued by adding bromine to the polymer solution, to give a brominated polystyrene, using the same catalyst for the bromination as for the polymerization. The Naarmann, et al. patent also refers to German Pat. No. 1,570,395 as concerning heat-stable styrene polymers obtained by polymerization of nuclear-brominated styrene, although no details are given. Elsewhere in the chemical literature, the cationic polymerization of para-bromostyrene has been reported; J. Prakt. Chem., 314,557 (1972).
The literature also refers to the clay-catalyzed cationic polymerization of styrene in a mixed solvent such as toluene and 1,2-dichloroethane and reports that a major fraction of the saturated ends of the resulting polymer are methylphenyl, formed by condensation with solvent toluene; J. of Pol. Sci.: Part A, Vol. 2, pp. 221-31 (1964).